In recent years, from the point of view of the prevention of global warning, energy conservation has been studied in various fields. Also in information equipment such as an image forming apparatus, efforts such as electric power saving in standby mode are underway so that the above image forming apparatus can be used at low energy, and further, in a fixing process in which energy is consumed in highest amounts, methods for such as lowering a fixing temperature have been studied. Lowering a fixing temperature decreases energy required for the fixing itself, as well as reducing a warm up time (WUT).
The final goal of lowering a fixing temperature is achieved by a pressure fixing method, in which a fixing is carried out only by applying pressure without using heat at all, and the method has been studied (refer, for example, to Patent Documents 1 and 2).
However, in a fixing method, in which both heat and pressure are applied, a fixing can be achieved with small pressure, since pressure is applied to toner particles which are in a state of being melted and deformed by heat, but in a pressure fixing method, high pressure is required to be applied to toner particles, since the toner particles have to be plastically deformed only by pressure. As a result, an apparatus having a larger size or heavier weight is required. Further, in case where a paper is used as an image support, since irregularity exists on the surface of the paper due to paper fibers of larger scale than a toner particle, it is necessary to apply considerably high pressure to uniformly plastically deform toner on the paper. However, in case where a fixing is carried out at a high pressure to the extent that toner is uniformly plastically deformed on the paper, the damage on paper is heavy to result in a problem that a high quality print can not be obtained.
As a method for solving such a problem, a method for using microcapsule toner is disclosed in, for example, Patent Document 3. However, in case where capsulation is insufficient, there exists a problem that a core material oozes out resulting in generation of toner aggregation in a development apparatus.
In Patent Document 4, it is disclosed that a viscous material, such as resin and ethylene vinyl acetate copolymer resin (EVA) exhibiting viscosity at the normal temperature and a low glass transition temperature (Tg), is introduced into a core material of toner particles to improve fixing property to paper. However, in such toner, it was difficult to obtain sufficient heat resistant storage properties.
In a method using such microcapsule toner, it has been studied for toner particles, having core particles comprising a resin component and a shell layer covering the core particles, to improve fixing properties by making the shell layer thin (refer to Patent Document 5). However, there exists a problem that sufficient heat resistant storage properties can not be obtained without having a certain degree of thickness in the shell layer.